How Much Thermal Camera Do You Need?

THE LATEST FRUIT from drone maker DJI’s partnership with FLIR Systems, the world’s largest commercial thermal imaging manufacturer, means that you can now acquire a UAS with a fully integrated thermal camera for less than $3,000. The DJI Mavic 2 Enterprise Dual (M2ED) is a breakthrough in terms of price—and therefore access—to this technology.

It is crucial, however, to understand what you are actually getting for that money, what it will do, and what it won’t do for you. The key factor that distinguishes the M2ED from, say, a DJI M200 equipped with a ZenMuse XT2 thermal imaging camera gimbal (apart from $15,000) is the thermal sensor’s resolution.

The XT2 incorporates a FLIR Tau2 camera core with a 640 × 512-pixel resolution. The M2ED incorporates a FLIR Lepton camera core with a 160 × 120-pixel resolution. If that sounds like a big difference, it is. It impacts the fundamental suitability of each aircraft to perform certain types of missions.

Resolution Solution

Let’s begin by understanding why all thermal cameras have such low resolution compared with their visible-light counterparts. Although 640 × 512 is significantly more pixels than 160 × 120, they are both laughably small compared with the 3840 × 2160 pixels offered by the 4K cameras that are standard on drones and cellphones these days.

To understand why, we need to revisit high school physics. The reason red, yellow, green, blue, and violet look different to us is the wavelength of the light waves striking the cones on our retinas. The reason we can’t see infrared or ultraviolet light with our own eyes is that the wavelengths are too long and too short, respectively.

These differences are not merely a point of trivia; they have real-world impact on how imaging systems work. In the infrared spectrum captured by thermal cameras specifically, the wavelengths are so long that the individual pixels on the sensor need to be physically larger in order to capture them.

Larger individual pixels mean that fewer of them fit within a sensor of a given size. Thermal and visible light cameras of comparable physical dimensions, such as what we see side-by-side on the M2ED’s gimbal, have a huge disparity in resolution. That’s also why we will likely never see a relatively high-resolution thermal camera integrated into the gimbal of a Mavic-size drone. It simply won’t fit.

Good Enough?

Whether a $2,700 M2ED is sufficient to accomplish your mission or you need to spend $17,600 for an M200 with an XT2 depends on your mission’s parameters. As you can see in the accompanying images, the difference in quality is substantial, but you’re not going to spend thousands of dollars on a drone with a thermal camera because you want to look at pretty pictures.

You need to decide whether it is going to provide the information you need for your particular situation. To help you choose, I’d like to suggest this paradigm: A low-resolution thermal camera is good at telling you whether or not something exists, whereas a high-resolution camera has a better chance of telling you what it is.

For example, let’s say you’re a first responder who has rolled up to the scene of a car crash along a snow-covered road. The vehicle is unoccupied, and you suspect that the driver or possibly a passenger might have been ejected by the force of the impact. If anyone survived, you need to find the person or people quickly before they succumb to their injuries or hypothermia.

A low-resolution sensor, such as the one incorporated into the M2ED, will help you find a thermal target—a living human being—but it won’t tell you much else. Is the person short or tall? How is he or she dressed? In that moment, those details are irrelevant. The only question that truly matters is where the person is.

Sweat the Details

Conversely, let’s say that you’re inspecting the heat exchanger on a rooftop air conditioning unit. You need to be able to distinguish between different components of a single mechanical system. Being able to see and recognize details is essential to the mission’s success. If the air conditioner is merely a blob of pixels, you aren’t getting the information you need.

You could fly closer to the object but doing so increases the risk to your drone and might also put it outside of your direct line of sight, creating a regulatory issue while simultaneously increasing the possibility of interference with your control, video, and telemetry signals.

Keep in mind that the best drone is the one that you have with you when the need to capture an aerial perspective arises. The Mavic is lightweight and portable, meaning it can easily be tossed in the trunk of a patrol car or the cab of a fire engine, ready for immediate deployment. The M200 is larger and more cumbersome, potentially making it better suited for planned missions.

The success or failure of a single drone mission or an entire drone program is not directly dependent on the money spent or the features and capabilities of the aircraft, but whether it delivers the required information in a timely manner and a usable format.

Did You MSX Me?

FLIR recognizes that whether it’s 640 × 512 or 160 × 120, thermal imaging systems do not offer the sort of resolution people expect from modern cameras. Furthermore, thermal cameras lack some fundamental capabilities that we take for granted when working in visible light, such as the ability to read a street sign or the safety placard on a hazardous material container.

The company developed and patented its Multi Spectral Dynamic Imaging (MSX) technology as a partial solution to this problem. On the M2ED, the thermal camera isn’t paired with a 4K video camera simply so you can do work on the side as a low-budget aerial cinematographer. MSX combines the imagery from the visible and thermal cameras to enhance your ability to recognize objects in the environment.

Specifically, it runs a real-time edge-detection algorithm over the visible light image and superimposes those edges on the thermal image. Surface markings become visible, and details in the thermal image become easier to place in their proper context because you are now able to see and recognize familiar shapes.

Know Your Limitations

The most crucial thing to recognize about any thermal imaging system is that it’s not magic. Just like visible light imaging, it adheres to the rules of physics, which puts limits on its capabilities. For example, movies and TV shows often show secret agents using thermal imaging to peer through walls and see people moving inside a structure.

In real life, it doesn’t work that way. Indeed, although visible light passes right through window glass, for example, the same material reflects infrared photons. Not only are thermal cameras unable to see through walls, they aren’t even able to see through windows.

If you understand its limitations, as well as the type of information you can reasonably expect to get from thermal cameras with different image resolutions, you can use it to accomplish amazing things, especially when coupled with the aerial perspective that drones provide.